1. Field of the Invention
The present invention generally relates to computer networks and servers and more particularly to a method for balancing network loads among multiple servers.
2. Background of the Invention
It is often desirable to connect multiple server computers to one or more external networks. Balancing of data traffic loads is often desirable when multiple servers are interconnected. Load balancing involves either distributing traffic to the servers so that all servers have approximately equal ratios of traffic volume to traffic handling capacity or, when traffic volume is low, reducing power to some servers while others handle the traffic. Traditionally, load balancing of a number of servers is achieved by connecting them to a dedicated, external load balancer box. Traditionally, algorithms programmed into the circuitry of a dedicated load balancing box can distribute traffic to the servers in a predefined manner that does not account for individual server load. Some load balancing boxes use the number of connections opened on each server as an indicator to assume load ratios on servers. More expensive and modem load balancing boxes interact with special software agents loaded on servers to collect rudimentary resource utilization information from the servers and use the information as feedback to distribute the loads. Traditionally, load balancer boxes are used to distribute loads to tens of servers. With computer technology advances, newer servers can handle many more loads than older ones, and new classes of servers have also emerged, e.g., web cache, streaming media cache, and virtual private network (VPN). These new classes of servers are typically used together in lower numbers, e.g., less than five. Therefore, using the same type of load balancer boxes for newer generations of servers is expensive, since a load balancer box can cost thousands or tens of thousands of dollars. In addition, the load balancing box represents a single point of failure. That is, if the box fails, all servers connected to it can lose connectivity to the external network or networks. To overcome this problem, more than one (redundant) load balancing box is typically used. This makes the cost problem even worse.
Alternatively, when only a few servers are to be deployed, low-cost load balancing can be achieved through a load balancing circuit board, such as a PCI card, installed in a computer, where the board has multiple network ports that connect to multiple servers. Load balancing circuit boards are typically designed for low-cost deployment, so they have simpler load balancing algorithms than the expensive load balancing boxes. Load balancing circuit boards available in the industry today, such as SonicWALL's Load Balancer—PCI card, typically use a “fan-out” configuration in which one board distributes loads to as many as four directly attached servers, but more servers can be attached by using additional hardware switches. To achieve redundancy, a primary board on one server can be coupled with a secondary board on another server in case of failure of the primary board.
It would be desirable to have a low-cost and scalable method of interconnecting multiple servers and connecting the server group to an external network or networks. A low-cost load balancing card can be designed to be resident within a server. Multiple load balancing cards can be connected in a daisy-chain configuration when there are only a few of them or to a non-load-balancing switch when there are several of them. In a daisy-chain configuration, a network connection is made to a first board, a second board is connected to the first, a third is connected to the second, and so on. In this configuration, if one board fails, the boards farther along the chain lose their connection to the network.